Theftproof lamp socket



June 1s, 1940. BELANG 2,204,666

THEFTPROOF LAMP `SOCKET- Filed Feb. 6, 1940 linien/Zar ma# Mm l Patented June 18,1940` PATENT oFFicE `'runs'riendoF LAMB socns'rf Leonard Delano, yMinneapolis, Minn..` V s Application February 8, 1940, Serial No. 312880 l '1 claims. (C1. Haasse) s My` invention relates to sockets for electric light bulbsand particularlyto `sockets `arranged tdprevent theft of lamp` bulbs therefrom.

,Much diiculty and expense `has been occat, sioned ldue, to theft of electric light bulbs from lamp sockets ofconventional design situated `in s places' accessible to the public such as public telephone booths,halls `and toilet rooms of public ibuildings and apartment buildings,` and the l0 like. wTo prevent .such thefts lamp guards which are lockedl onto sockets have been used and various types of special` lamp sockets have been devised@` .i i

`Lamp sockets have been devised wherein lamps L51 `are retainedlby means which are releasable by suitable application of` keys or tools thereto and suchsockets work iny thesame manner regardless `of whether the lamps therein are burned i out or` are inoperable condition. Such sockets have the `disadvantage that the necessary key or tool may be lost or not at hand `when, a change of lampsbecomes necessary. i ALgeneral object of Lmy invention is to provide alamp `socket from which a burned out lamp may `be, easily removed without the use of a key or mit removal of only a burned out lamp.

, Another object is to provide such a socket in- 1 cludinga screw base lampsocket mounted in a ,socket` case for rotationrelative thereto about theaxis of the socket element so that the socket element will tend to turn with a lamp bulbwhich is `inengagement `with the screw threads `of s the socket element and being rotated relative to the socketcase.` i i s Still another object is to provide such a socket including means limiting rotation of the socket element` responsive to screwing of a lamp thereinto but permitting rotation of the socket resu sponsive to an attempt to unscrew a lamp there- `from. n s Y i i Yet another object is to provides such a socket having normally inoperativemeans for limiting rotation of the socket responsive to unscrewing rotation ot a lamp in the socket `relative to the socket `case controlled by electromagnetic means brought into action by a switch manipulatable tool and; from which an operable lamp cannot ingi-.inemoval of an` `operable lamp `from the the burned out lamp and an operablelamp to perroln `outsidethe` socket case to render said ,ro-

tation limiting` means operative if` the lamp in the socket is burned out and leavegsaidrotation limiting means inoperative if the `lamp in the socket is in` operable condition. s

i A` further Objectis to provide such a lamp socket of which all the rotation controlling parts andthe socket element, are suiliciently compact to enable housingof` the same in` a. socket case of dimensions not exceeding the dimensions of the` case of a `conventional lamp socket to an impractical extent.

A stillfurther object is` to provide such aitheftproof lampi socket of light, simple, rugged, re-` liable andfinexpensive construction.`

, These` and other objects and advantages of the invention will more fully `appear from the following description made connection with the` accompanying drawing, wherein likereference characters refer tothe same partsthroughout the views, and, in which; i

i Fig, 1 is a` longitudinal sectional View `cfa theftproofzlamp socket `which constitutes an:` ernbodiment of my invention; s 1 1 Fig. 2` isoasectional View` taken ontheline 2N`-2ofFig.1; i f M s Fig.` 3 is a partial side view;

, Figl isan" explodedview of a group of movable elements employed inthe socket rotation controlling mechanismof my theftproof socket;

Fig. 5f is. anelectrical connection diagram `of socket element, electromagnetic control` means and `electricalswitching means of my `theitproof lamp `socket.

, Referring tothe drawing, I provide a socket case l0 consisting` of atubular. bodyportion la andacap portion IUb which may be constructed s in the same manner as a` conventional lamp socket case and in which the body low and cap IDD may be connected together in the same manner asithe corresponding partso-f a conventional lamp socket case. Howeven the dimensions` of my `socket ,case I0 are somewhat greater than` those -of theV conventional lamp socket case so and which will be` described.`

In the Ylower and open `end ofgthe `case IIJ, I provide a lamp socket `ll of the Edison or screw 'base type supported withinthe lower portion` of the case l0 forrotation relativetthereto about thecommon axis of the case `Ill `and `socket element Il. The socket elementdncludesan elecas to accommodate the parts contained `therein trically conductive screw `fshell lla similar to that of `theordinary lamp socket and having ani inwardly flanged upper end to which a centrally apertured disc IIb is secured by suitable means such as the rivets IIc. On the lower side of the center of the disc I Ib I provide a center electrical contact button Ild corresponding to the center contact button. of the ordinary lamp socket and formed. in a manner to be described.

For rotative mounting of the socket element II I provide a shaft I2 disposed thereabove in co-axialv relation therewith. the shaft I2 is made to reduced diameter, is extended downwardly through the ap'ertured central portion of the disc IIb and is peened or riveted at its lower end to secure the disc IIb of the socket elementl II to the lower end of the shaft I2 and form the center contact button II d of the socket element II as shown. Thus the shaft I2 and socket element II are non-rotatively connected for rotation together as a unit.

The shaft I2 is journalled and in electrical contact with an electrically conductive and preferably but not necessarily non-magnetic sleeve I3 which constitutes a stationary bearing for the shaft I2 and electrical Lterminal for the center contact button IId of the rotatable socket element II. The lower end of the sleeve I3 and the disc IIb ofthe socket element II are spaced `apart by acollar I 4 formed of electrical insuy proximately flush with the upper end. of the sleeve I3. A centrally apertureddisc I5 of electrical insulating material is iixedly mounted on c coil M is wound on the sleeve I3 and the shaft.

the lower extremity of the sleeve I3 by suitable means such as by screw threading the sleeve I3 and disc I5 as indicated in` Fig. 1 of the drawing. A helical spring I6 lis placed in encircling' relationwith the insulating collar I4 and interposedv between the insulating disc I 5 and flanged upper end of thev screw shell IIa of the socket element II in partially compressed condition so as to be in firm electrical contact with the screw shell 'IIa of the rotatable socket element I I to provide a stationaryy electrically conductive means connected withy the screw shell IIa in a manner not interfering with rotation of the socket element II. The wire of which the spring I6 is formed is extended to form an electrical conductor I6a running along the inner side of the tubular socket case member Illa to the upper'portion of the interior space of the socket case III. The electrical conductor IEa may,v of course, be provided withan electrical insulating covering'in any suitableconventional manner to prevent undesired electrical contact thereof with other parts of my device.

A short distance below the upper end of the sleeve I3 a centrally apertured electrically con,

ductive plate I 'I is xed thereon in encircling relation therewith in a plane normal to the common axisv of the sleeve I3 and socket case III. Immediately below the plate I'I a centrally apertured disc I8 is placed on the sleeve I3. Between the insulating discs I5 and I8 an electromagnetic I2 constitutes a magnetic core for the coil M for a purpose to be later explained. The coil M is wound fork use as a potential coil to be operated on the samey voltage as a lamp to be placed in the socket element II.

' A second electromagnetic coil S is provided in upwardly spaced and co-axialrelation with'the- The lower end of` first coil M and has therewlthin a magnetic core I9 disposed co-axially of the shaft I2 and having a lower endl spaced a short distance above the upper end of the shaft I2. A pair of upstanding posts 20 formed on the right-hand portion of the plate I'I and another pair of upstanding posts 2l formed on the left-hand portion (as viewed in Fig. 1) of the plate I'I engage, at their upper ends, the lower sideof the upper electromagnetic coil S tomaintain the same in a xed spaced relation with the plate I'I. The coil S is wound for connection in series with a lamp carried in the socket element I I to operate on current passing through the coil S to such lamp.

Above the upper coil S I provide a spring return, single pole, double throw electrical switch 22, which may be of any suitable conventional construction and which includes an operating button'22d therefor which projects through `a suitably apertured portion of the tubular socket case member Illa to Aa point outside thereof asy indicated in Fig. l.` As in any conventional type'y of socket I provide for bringing an. electricalv cord such as the cord `23 into the upper end of the interior space of the case III for connection of the individual electrical conductors 23a and 23h thereof to suitable terminals of my device. The electrical connections between the crd2ZI,'-r the switch 22, the coils Sand M and the socket element IIare diagrammatically shown in Fig. 5 and may be'formed of suitable electrical con-` ductors of conventional type installed in`my' The remaining terminal of` the coil SY is con nected to the stationary contact element'22c ofthe switch 22 which is normally engaged by the' movable switch contact element 22h and is also y connected to the plate I'I and accordingly through the sleeve I3, and the shaft 'I2 to the center contact button IId'of the socketelement II.

'Ihe switch contact element 22d, which is nor'` mally not in engagement with the 'movable switch contact element 22h is connected to the remain-l ing terminal of the coil M. Fromthe above it should be seen that the coil rS is connected' inv series with the socket element II but is nor` mally shunted by the normally interengaged switch contact elements 22h and 220, and that the coil M is soconnected as to normally bei de-energized. Shifting of the movable switch contact element 22h froml normal position to op' erated position will rstrunshunt the coil S to cut the same in series witha lamp inthe socketr be provided for connection of the cord conductors 23a and`23b thereto andwill, of course, be connected in turn to the above described electrical circuit elements of my device iny accordance with A centrally apertured control disc' 26, best shown in Fig. 4, is placed on the reduced diam` eter upper end of. the shaft I 2 and is` xeduon -I the shaft I2 by peening or riveting the reducedv i handnotchI-Za, of fthedisc 26 as viewed` `in Fig. 4`

i One`notchg26a, would provide 'for the .intended operation ofmy `device `but-I` prefer to `provide two notches 26a, and, if desired, could provide alarger Anumber. i Of the nearlyyradial` edges of thetdisc 26d`efiningeach notch 26a, I Ibevelyas shown, the' lower .-side of the` one nearly radial edge situated at the right-hand side of the leftto` form `an inclined camming `surface `21512. The nemainingnearly `radial ledge 2Bcuis `purposely not bevelled llandconstitutes an abutment surface.

, il provide imeans co-.acting with `the control disc' 26 to limit rotation of the socket element Il such :as wouldbecaused by anattempt to screw awlamp ,into'fthe socket element II. For this .pur-posed iprovide a flat, resilient, annular, upwardly pressing :spring `2l, best shown in Fig. 4, disposed in encircling relation with the upper end portion of the bearingfsleeve I3. At one side :of itheannular spring the same is extended outwardly to 4:form an apertured mounting ear 21e which, `as ,seen in Fig.` l, is placed on the left-:hand portion of the plate `Il and is xedly secured `thereto by suitable means such as` the rivetsZ'If. Diametrically `opposite 'the mounting year-2i|e, that `is 4at the de-ilectible free edge portionof the spring 21, the spring 21 has secured "E'Ibfor coeoperation with `the inclined camming surfaces 2Gb ofthe notched vportions of the control disc 26.4 The edge lof the block 21a. opposite `the bevelled portion 2lby thereof is `left unbevelled to `constitute: an abutment surface 21C. Due to the upwardly `.pressing construction of the spring 21 itheinner portion of the `block 21a is pressed `againstthe `lower `side of the control disc 26 and, asthe disc 2B is rotated, the block 21a moves upwardly into a notch 26a of the control disc 26 `.when ithenotch ,26d becomes disposed above the blockqZ'Ia. When the control -disc 2.6 is rotating in the direction lin which `the `socket element II would :be carried by an attempted screwing of yailamp linto `the socket element II, engagement yofttlie `block 21a in one of the notches 26a would result inwinterengagement of `the abutment suracesv26c and 21e ofthe control disc l26 and the blocklla `to prevent further rotation of the socket element II and thus enable screwing of theilamp'into the socket `element II. To `re'- strainthe spring"2l and block 21a from displacement circumferentially of the 4spring 2ll the outer portionZ'ld `of the block 21an is disposed between theupstanding elements 20 which are spaced apart to` closely receive the block portion 21d for `guiding the same in vertical movement and restraining the same from movement circumferen- A`tially`oiitl'le annular spring 2l, When the con-` trolf-discis rotatingin` the direction correspondingito the direction in which the socket element ISI would be"rotate`d responsive 4to an attempt to yunscrew a lamp from the vsocket element, the block 21a `willraise into anotch 26a ofthe control disc 25 eachtime a notch 26a. is over the block 21a but the camming surfaces 28h and 2'Ib of the control disc 26 and the block 21a will interact to force the block 2.1 downwardly out of the notch 26a so that `there will. be no restraint of rotation ofthe control disc 2B `and the socket element `II to permit unscrewing of a lamp `from the socketelement II. Thus rotation of a lamp in'rthe ysocket lelement `II in a direction intended to bring about unscrewing of the lamp from `the socket `element I I will merely resultiin the socket element II rotating `with Ythe lampto defeat removal of the lamp frornthe socket element II.

I provide means, partiallydescribed above, for

.enabling limiting `of rotation ofthe socket element yII whenan attempt is made to unscrew a burned out lamp from the socketielement I I and whichwill not act to limit rotation of the socket element II when an attempt is made to remove an operable lamp from the socket element II. For this purpose I `provide a vertically deilectible magnetic armature 28 `above the control ldisc 26 and `between the electromagnet poles constituted `by the upper `end `of theshaft I2 and the lower end of the core I9 of the upper electromagnet S. `As 'best seen in Fig. 4, the armature 28 has, kon

one end `thereofa pair of lugsZtla apertured to accommodate a pivot pin. At the left-hand (as viewed in Fig. `l) side of vthe plate `I'I the same is provided with an 4upstanoling member `2!! to `the upper end of which the armature .pivot lugs 23a .are pivotally connected by means of a pivot pin 30 `so that :the armature 28 is mounted for vertical swinging movement between theupper end of the shaft I2 `and the lower end of the magnet core I9 in response to magnetization of one or the other thereof. `The free end portion 2819er the armature 28 is narrowed, as shown in Fig. 4, `so `that the .same may be disposed between the vertical posts 20 to be guided thereby in vertical movements Aand to 'be restrained thereby from `any appreciable `sideward movement. A very light `spring 31| is .provided .as` shown in Fig. `l to nor- `mally maintain the armature 28 yin an upwardly `deflected -position thereof. In position for cooperation with the notched portions of the control disc 26 when the armature 28 is deflected `downwardly,out of itsnormal upwardly deflected position, lthe armature 28 is provided with a stop element 28C which, as best seen in Fig. 4, projects from :the `free end portion of the armature 28,

slightly `above the control disc 26 when the arma ture 28 isin its normal upwardly deflected position.

When it is `desired to attempt to remove a lamp from the socket element II the lamp is rotated `in a direction intended for unscrewing of the lamp and at the same time theswitch 22 is shifted into and held in its `operated position to `first `cut the coil S` in series with the lamp socket element I I and then connect the coil M to the line` conductors 23a and 23h. If the lamp in the socket `element II is inoperable condition, cutting of coil S in series with the socketi'element II will result in current flowing through the -`coil S whereby thecore I9 thereof Awillbe'magnetized to hold the armature 28 in itsnormal upwardly deected position so that'subsequent-energization of the coil M, when the switch 22 reaches its fully operated position,`to magnetize theshaft I2 will not be effective for pulling the armature 28 into its operated position. Consequently'thestop element'28c Will remain ina position above the control disc 26 and rotation of the lamp will'result,

in unrestrained rotation of the socket element I i to defeat removal of the lamp from the socket element II. If the lamp happens to be 'burned out'or otherwise openA circuited, the series coil S Willnot be energized by operation-of the switch 22 since there will be no current'flowing through the coil S to the' burned out lamp* and consequently the only opposition to movement of the armature into operated position will bethe very light spring 3l which is purposely made too weak to prevent deflection of the armature' 28 responsive to magnetization of the shaft I2 by energication of the coil M. When the switch 22 reaches its fully operated position, the coil M will be energized to magnetize the shaft I2 which will then deflect the armature 28 downwardly with"- out opposition from the. coil S. As the control disc 26 is rotated,ione of the notches Zta thereof will reach a position under the stop element 28e of the armature 28 and the stop element 28C will drop into the notch`26aI clue to the magneticpull of the magnetized shaftl I2. Further `rotation of the control disc through a slight angle will result in the free end portion of the stop element 28C becoming disposed under a portion of the control disc 26 adjoining the notch 26a. and an edge 2619 of the disc 25 partially defining the notch `tot abuttingthe medialportion of the stop element 28e to prevent further rotationof the control disc 26 and the socketelement II 'so that the lamp may be unscrewed from the socket element II. After the free end portion of the stop element 28C has reached a position under part of the control disc 26 it is no vlonger necessary to hold the switch 22 in operated position for the reason that the armature cannot then rise since the free end of the stop element 28o is in engage.- ment with the lower side of the control-,disc 26. Thus it is seen that my theftproof socket device permits removal therefrom of a burned out lamp but defeats removal therefroml of an operable lamp. v l

When a new lamp is to be screwed into vthe socket element II, the socket element' II will, at first, rotate with the lamp. This rotation of the lamp socket element II will rotate thecontrol disc in such direction'that the free end -of the stop element 28o of the armature 281 vwill disengage from the control disc 26 whereupon the spring 3| will return the armature 2B to its normal upwardly deflected position. kFurtherrotation of the control disc 26 will 'bring into play the block 21a on the spring 2l to limit rotation `as previously described and thus enable vscrewing the lamp into the socket element II.

Since energization of the coil M is required in enabling removal of a lampl from my device it should be apparent that a lamp cannot be removed from my device when the supply'of electrical current to the entire device is shut off as by` means of a lighting switch in the circuit from whichthe cord 23 runs or a switch incorporated in the device ahead of the switch 22.

Attentionis called to the rfact that the switch contact 22e may beomitted from-the switch 22 ,S0 as to leave the coil ,15. permanently unshunted in lcasesy where the voltage drop caused-by the impedance ofthe coil S would `notbe 1objec. tionable. Also it is possible to omit the switch 22 entirely so as to leavethe coils S and M permanently in seriesand parallel respectively With the circuit to the socket element I I if the relative strengths of the coils S and M are such that the coil S, when energized,'is"sufficiently strong to attract the armature' 28- away from` the. coilv M; If my 'device is used in an inverted position it is,'of course, feasible to omit the spring -3I-:and permit thepull of gravityto take care of the function ordinarily provided by the spring' 3|.'

. It is apparent that I have yinvented a novel; effective, light, compact'reliable'and inexpensive theftproof electric lamp socket permitting installation of a lamp therein, capable of preventing removal of an operating lamptherefrom, and are l ranged to enable removal of a burned'out lamp therefrom by a single and easy manipulation which is performed without the use of anykind of ay key or tool. l f f It will, of course, be understoodlthat various changes may be made in the form, details, arrangement and proportions of the various parts without departing from the scopeof my invention. "Y f Y What is claimed is: f l. An electric lamp socket device for preventing removal of an operable electric lamp bulb therefrom comprising, an open endedcasing'ari electric lamp socket having the usual screw tation of said lamp socket,I normally inoperative` mechanism for limitingsaid opposite rotation of said socket, an electromagneticv armature in'- cluded in said mechanism and lconstitutinga control element therefor shiftable between actu'- ated and unactuated positions whereby `said mechanism is rendered respectively operative and inoperative, a first: electromagnet connected `in series with said socket and associated withsaid armature for operation to hold the same in unactuated position, and a secondelectromagnet connected in parallel withsaid socket'and associated with said armature for operation to tend to pull said armature into its actuated position, said lrst electromagnet being of sufficiently greater strength than said second electromagnet to be capable of attracting said armature 'away therefrom.

2. An electric lamp socket device for preventing removal of an operable electric lamp bulb therefrom comprising, an open ended casing, an electric lamp socket having the usual screw threaded lamp receiving element and being mounted in the open end of said casing for rotation :about the axis of saidfsocket, vmeans vlimiting rotation of said'socket with a lamp being screwed thereinto and permitting opposite rotation of'said socket, normally inoperative mechanism for limitingsaid opposite rotation of Said' socket, an electromagnetic armature included in saidmechanism and constituting a control element; therefor shiftable between actuated; andl unactuated positions whereby said mechanism is rendered respectively operative and inoperative, relatively Weak yieldable means for normally maintaining said armaassociatedwth Said armature for` operations@ ZA hold the same in1unactuatedlposition,` and a' sec- "oiid-' `electromagnet `connected in parallel with said socket and 1` associated with said` armature forop- `eration to 'l tend to pull said* armature i'nto its `actuated position, said iirst `electromagnet being ofWsuiciently `greater strength than said second electromagnedtobe capable of attracting said armatureaway therefrom;v 1 I i *3f An electricL lamp `socketldevice for preventlling removalff an operable lamp bulb therefrom comprising, Aa`n^open ended casing, an electric lamp `socketl'lavingthe usual screw `threaded lamp receiving element and being mountedv in the openl end of said 1casing for rotation about `the `axis of said socket, means limiting rotation of said socket with a lamp being screwed thereinto and permitting opposite rotation of said socket,` normally inoperative mechanism for limiting said opposite rotation of said socket, an electromagnetic armature included in said mechanism and constituting a'control element therefor shiftable between actuated and unactuated positions whereby said mechanism isk rendered respectively operative and inoperative, relatively weak yieldable means for normally maintaining said armature in its unactuated position, a iirst electromagnet connected in series with said socket 3 and associated with saidarmature for operation to hold the same iii unactuated position, a secondelectromagnet connected in parallel with said socket and associated with said armature for operation to tend to pull said armature into its actuated position, and spring return electrical switching means normally maintaining said second electromagnet disconnected, said switching means being operable from outside said casing to coni nect said second electromagnet.

4. An electric lamp socket device for preventing removal of an operable lamp bulb therefrom comprising, an open ended casing, an electric lamp socket having the usual screw threaded lamp l receiving element and being mounted in the open endof said casing for rotation about the axis of said socket, means limiting rotation of said socket with a lamp being screwed thereinto and permitting opposite rotation of said socket, normally inoperative mechanism for limiting said opposite rotation of said socket, an electromagnetic arma-M ture included in said mechanism and constituting a control element therefor shiftable between actuated and unactuated `positions whereby said mechanism is rendered respectively operative and `inoperative, relatively weak yieldable means for normally maintaining said armature in its unactuated position, a iirst electromagnet associated with said armature for operation to hold said armature in unactuated position, a second electromagnet associated with said armature for operation to tend to pull said armature into` actuated position, said first electromagnet being connected in series with said socket and `said second electromagnet being connected in parallel with said socket, and spring return electrical switching means normally shunting said iirst` electromagnet and maintaining said second electromagnet disconnected, said switching means being operable from outside said casing to unshunt said rst electromagnet and connect said second electromagnet.

5. An' electric lamp socket device for preventing removal of an operable lamp bulb therefrom comprising, an open ended casing, an electric lamp socket having the usual `screw-threaded lamp-receiving element and being mounted in the open end oi said casing for rotation about the axisof the` socket, adisc having an eccentrically situated recess therein,"said disc `being disposed co-axially of` said socket and mechanically connected thereto in `non-rotative relation therewith, means `associated with said disc for cooperating with the recessed portion thereof to limit rotation of said socket witha lamp being screwed thereinto and permit opposite rotation` of said socket, an electromagnetic armature situated adjacent said discand having a portion engageable in said recess when said armature is in `actuated `position to limit said opposite rotation, relatively `weak yieldable means for normally maintaining said armature in an unactuated position thereof, a rst electromagnet connected in series with said socket and associated withsaid armature for'operation to hold the same in unactuated position, a second electromagnet connected in parallel with said socket and associated with said armature for operationto tend to pull the same into actuated position, and spring return electrical switching means normally maintaining said second electron magnet disconnected, said switching means being operablefrom outside 'said casing to connect said second electromagnet.

6. An electric lamp socket device for preventing `removal of an operable lamp bulb therefrom comprising, an open ended casing, an electric lamp when said armature is in actuated position to limit said oppositerotation, relatively weak resilient means for normally maintaining said armature in an unactuated position thereof, a first electromagnet connected in series with said socket and associated with said armature for operation to hold the same in unactuated position, a second electromagnet connected in parallel with said `socket and associated with said armature for operation to tend to pull said armature into its actuated position, and spring return electrical switching means normally shunting said first electromagnet. and maintaining said second electromagnet disconnected, said switching means being operable from outside said casing to unshunt said i'lrst electromagnet and connect said second electromagnet. i

7. An electric lamp socket device for preventing removal of an operable lamp bulb therefrom comprising, an open ended casing, an electric lamp socket having the usual screw-threaded lamp-receiving element and being mounted in the open end of said casing for rotation about the axis of the socket, a disc having a rectangular notch in the marginal portion thereof, said disc being disposed co-axially of said -socket and mechanically connected thereto in non-rotative relation therewith, means co-operating with the l notched portion of said disc to limit rotation of said socket with a lamp being screwed thereinto consisting of a rectangular element` situated and proportioned to t in the notched portion of said disc and resilient means carrying said rectangular element and pressing the same toward said disc, 75

the corner of said rectangular element' toward said disc and toward the direction of said rotation being bevelled to form a camming surface, the edge of said disc partially defining said notch and facing opposite said direction of rotation beingbevelled at the corner thereof nearest said rectangular element to form a camming surface for co-operation with said first-mentioned camming surface to cam said rectangular element out of said notch yresponsive to rotation of said discln a direction opposite to the direction of said first-mentioned rotation, an electromagnetic armature situated adjacent said disc and having a portion engageable in said notch when said armature is .inactuated-postion tdll-mit said opposite rotation, relatively weak resilient means- 

